What does it mean?
OBD II fault code P0243 is a generic code that is defined as “Turbocharger (TC) wastegate regulating valve “A” – circuit malfunction, and is set when the PCM (Powertrain Control Module) detects a malfunction in the control and/or signal circuit of the valve that regulates the operation of the turbocharger wastegate. The sole purpose of a turbocharger is to compress the intake air the engine uses to increase power delivery and improve fuel economy, particularly on small-displacement engines.
As a practical matter, a turbo charger consists of two chambers that are separated by a metal division- one chamber containing a turbine wheel, and the other containing a compressor wheel that is attached to the turbine wheel with a shaft that passes through the division. The turbocharger is therefore a self-contained assembly that is attached to the engine in such a manner that the exhaust gas exiting the engine has to pass through the chamber containing the turbine wheel.
In terms of operation, the exhaust gas that exits the engine serves to drive the turbine wheel, which then drives the compressor wheel that is attached to the other end of the shaft. As the engine speed increases, the volume and velocity of the exhaust gas also increases, thereby increasing the speed of the compressor wheel to the point where the intake air is highly compressed by the compressor wheel before it enters the engine.
This is known as the “boost pressure”, which has to be controlled to prevent engine damage caused by over boost conditions. While design specifics of these control measures vary slightly between manufacturers, the most common such measure involves dumping excess pressure into the exhaust system via a controllable valve that is built into the turbocharger casing, and which is known as a “wastegate” that can be controlled either electronically, or with a system that uses engine vacuum.
Regardless of the actual control mechanism though, the PCM obtains input data either from a dedicated boost pressure sensor, or from the MAP (Manifold Absolute Pressure) sensor. In both cases, the resistance of the sensor changes in response to changes in the boost pressure, which changes the PCM then interprets as actual pressure values.
Thus, when the PCM detects a pressure value that approaches or exceeds the maximum allowable boost pressure, it activates a control valve/mechanism that opens the wastegate to dump excess boost pressure into the exhaust system.
In a fully functional boost control system, the PCM will activate the wastegate control valve/mechanism continually, and to varying degrees in order to maintain the boost pressure at the optimum level (for that particular application), taking into account the engine speed, throttle position, throttle pedal position sensor, rate of throttle movement, and several other values such as intake air temperature, among others.
Thus, if the PCM detects a malfunction in the turbocharger wastegate control valve’s control and/or signal circuits, it recognizes that it cannot control the boost pressure effectively, if at all, and it will set code P0243 and illuminate a warning light as a result.